The phenomenal growth of international schools in Thailand in the past two decades has brought into focus not only the distinctive role of principals, but more importantly, the competencies that they should possess to be able to successfully manage these schools. Identification of priorities of these competencies, particularly by stakeholders like administrators, faculty and support staff is crucial in determining the quality of instruction in the institution under the stewardship of these principals. This study was conducted 1) to determine the level of importance of the key competencies of principals in terms of the following domains: policy and direction, teaching and learning, staff, partnerships and managing resources, 2) to determine the significant differences in the level of importance of the competencies as perceived by administrators, academic and non- academic support staff, and faculty and 3) to investigate the significant relationship among the competencies.The population of this study consisted of 95 international schools. Convenience sampling was used to select 105 respondents from six (6) schools. A questionnaire was developed and pilot tested to determine its validity and reliability.The statistics used to answer the research questions were 1) mean, 2) standard deviation, 3) standard error of the mean, 4) coefficient of variation, 5) ANOVA and 5) Pearson Product-Moment correlation.The research investigation yielded these results:1) The highest level of importance of the competencies of principals in international schools was in the domain of “policy and direction”. The lowest was in the “teaching and learning” domain.2) There were no significant differences in the level of importance of the key competencies of principals as perceived by administrators, academic and non-academic support staff and faculty.3) Significant relationships were found among the five (5) competencies of principals in international schools.